As used here, pinch shock describes a tire condition that can result when the tread section of the tire is impacted in a manner that causes the shoulder section of the tire to contact the bead section. In such condition, the sidewall of the tire is buckled or folded over itself as the shoulder section makes contact with the bead section. During such pinching, the rubber mix and carcass layer of the tire composite structure are compressed between the rim and an obstacle or other feature in the travel path of the tire. Under certain conditions, such as a severe impact, the carcass layer cords may undergo an extension beyond their rupture strength. It has been observed that pinch shock often results in the cords being severed in two different places in the carcass layer—one within the shoulder section of the tire and one at the bead section. Such severing of the cords in the carcass layer is undesirable because the cords contribute to the structural integrity of the tire. Depending on the number of cords that are broken, the tire may show a deformation or a cut.
In general, poor road conditions or other factors causing severe impact on the tread section of the tire can be responsible for pinch shock. For example, unpaved or poorly paved roads may have a variety of holes or other sudden changes in elevation that can lead to pinch shock. Similarly, roads containing debris or other obstructions can cause pinch shock as the tire encounters such obstacles in the road. Accordingly, for road surfaces where conditions leading to severe pinching of the tire are anticipated or expected, a tire more resistant to the breaking of radial plies is desirable.